Method of forming polycrystalline silicon layer on substrate by large area excimer laser irradiation

ABSTRACT

A method of forming a polycrystalline silicon thin film improved in crystallinity and a channel of a transistor superior in electrical characteristics by the use of such a polycrystalline silicon thin film. An amorphous silicon layer of a thickness preferably of 30 nm to 50 nm is formed on a substrate. Next, substrate heating is performed to set the amorphous silicon layer to preferably 350° C. to 500° C., more preferably 350° C. to 450° C. Then, at least the amorphous silicon layer is irradiated with laser light of an excimer laser energy density of 100 mJ/cm 2  to 500 mJ/cm 2 , preferably 280 mJ/cm 2  to 330 mJ/cm 2 , and a pulse width of 80 ns to 200 ns, preferably 140 ns to 200 ns, so as to directly anneal the amorphous silicon layer and form a polycrystalline silicon thin film. The total energy of the laser used for the irradiation of excimer laser light is at least 5 J, preferably at least 10 J.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface treatment method and asurface treatment apparatus.

More particularly, the present invention relates to a method of forminga thin layer of polycrystalline silicon on a substrate, and to a methodof forming a channel of a metal insulation semiconductor (MIS)transistor using the method of forming a thin layer of polycrystallinesilicon. Also, more particularly, the present invention relates to asurface treatment apparatus such as a laser light emitting apparatusadaptive to perform, for example, a laser light annealing treatment,where the area of irradiation by a single shot of laser light isrelatively large and an energy density of irradiated laser light ishigh, to thereby form, for example, a thin layer of polycrystallinesilicon from an amorphous silicon layer.

2. Description of Related Art

First, the formation of a thin layer (film) of polycrystalline siliconon a substrate of a transistor will be described.

Thin film transistors (hereinafter referred to as TFTs) using amorphoussilicon or polycrystalline silicon thin films are used for thetransistors for driving pixels in liquid crystal displays, thetransistors of peripheral elements, load element type static RAMs(hereinafter referred to as SRAMs), etc.

Polycrystalline silicon, however, has a higher density of unbonded armsof silicon atoms compared with monocrystalline silicon, so theseunbonded arms become the cause of generation of a leakage current at thetime the transistors are switched off. As a result, they become a causeof a reduced operating speed at the time of switching the transistorson. Accordingly, to improve the characteristics of a TFT, it is demandedto form a polycrystalline silicon thin film with few crystal defects andsuperior uniformity. As a method for formation of such a polycrystallinesilicon thin film, the chemical vapor deposition method and thesolid-state deposition method have been proposed. As the means forreducing the unbonded arms causing leakage current etc., use is made ofthe hydrogenation technique of doping hydrogen in the polycrystallinesilicon thin film so as to cause hydrogen to bond with the unbondedarms.

If the chemical vapor deposition method is used for growing large grainsize crystals and forming a polycrystalline silicon thin film, however,the thickness becomes nonuniform. With the chemical vapor depositionmethod, it is difficult to obtain a polycrystalline silicon thin filmwith a uniform thickness. Accordingly, it becomes difficult to formtransistors with uniform device characteristics using a polycrystallinesilicon thin film.

Further, with the solid-state deposition method, it is possible to growdendrites and form a crystal with a grain size of at least 1 μm, but thedendrites include small defects such as dislocation and twins which actas traps to obstruct improvement of characteristics and destabilize theoperation.

To reduce the grain boundary trap density due to the unbonded arms,there has been proposed the method of performing annealing treatmentusing excimer laser light. Excimer laser light has the advantage of alarge coefficient of absorption in silicon due to the UV light and canheat just the area near the surface of the silicon. Accordingly, thereis no effect on the underlying layer, i.e., glass substrate, bottomlayer LSI bonding portion, etc.

As methods for excimer laser annealing, there is known, first, themethod of direct annealing of the amorphous silicon film and, second,the method of annealing by excimer laser light by an energy density atwhich the film as a whole will not melt.

The former method of direct annealing of the amorphous silicon issimpler as a process compared with the latter method and is advantageousfor the future mass production of LSIs. Further, if a large area can beannealed by a single irradiation of the excimer laser light, this wouldbe further advantageous for mass production.

When use is made of such excimer laser for directly annealing anamorphous silicon film, however, it is difficult to obtain an excimerlaser beam able to cover a large area in a single shot and havingin-plane uniformity sufficient for obtaining a polycrystalline siliconthin film having a low grain boundary trap density and a goodcrystallinity. To make up for this, an excimer laser having a largeoutput energy able to anneal a large area with a single shot has beenunder development in recent years. Further, to improve the effect of theexcimer laser annealing, it has been considered to heat the substrate toseveral hundred degrees for direct annealing of the amorphous silicon,but the process conditions for obtaining a polycrystalline silicon thinfilm having a low grain boundary trap density and good crystallinityhave not been specified.

Further, in the above method of direct annealing of amorphous silicon,the grain size of the polycrystalline silicon was less than an average50 nm.

Next, a surface treatment apparatus will be described.

When annealing a shallow region of a semiconductor substrate, use ismade of a surface treatment apparatus which is provided with a laseremitting laser light of a short wavelength, for example, xenon chlorideexcimer laser light of a wavelength of 308 nm. The energy of the laserlight emitted from a conventional excimer laser apparatus, however, islow, so it is not possible to anneal a wide area of about 30 mm×30 mmwith a single shot of laser light.

Accordingly, to perform laser annealing of a wide area, the practice hasbeen to form the laser light into a beam of for example about 0.6 cm×0.6cm to raise the energy density to about 0.9 J/cm² and to scan theannealing region with continuously emitted pulses of laser light.

If laser annealing is performed by this method, however, the time forthe annealing treatment becomes extremely long.

As shown in the explanatory view of the state of irradiation of laserlight in FIG. 1, since the laser light 121 is irradiated in severalpulses, the portion 141 connecting the region 131a irradiated by oneshot of laser light 121a (121) and the region 131b irradiated by thenext shot of laser light 121b (121) becomes discontinuous in terms ofthe amount of energy irradiated. Further, as shown by the graph of thedensity of irradiated energy and the irradiation position of FIG. 1, thelaser emission output fluctuates among the shots 121c, 121d, and 121e,so the uniformity of the annealing treatment becomes poor in some parts.Therefore, it was difficult to apply this technique to manufacturingprocesses of polycrystalline silicon thin films.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a surface treatmentapparatus and surface treatment method superior for annealing treatment,diffusion treatment, oxidation treatment, nitridization treatment, andother surface treatment by mounting a high output laser and irradiatinga broad area with a single shot of laser light.

Another object of the present invention is to provide a method offorming a thin layer of polycrystalline silicon which improves thecrystallinity.

Still another object of the present invention is to provide a method offorming a channel of a transistor superior in electricalcharacteristics.

According to the present invention, there is provided a method offorming a thin layer of polycrystalline silicon on a substrate,including: (a) a first step for forming an amorphous silicon layer onthe substrate; (b) a second step for exposing laser light to the heatedamorphous silicon layer in an extent greater than approximately 10 cm²by single shot exposure, the laser light having an energy density ofapproximately 100 mJ/cm² to 500 mJ/cm². Preferably, the laser light isemitted from a laser light emitting apparatus which has a total energyequal to or greater than 5 J.

The substrate may be heated to heat the amorphous silicon layer atapproximately 350° C. to 500° C.

More preferably, the method of forming a thin layer of polycrystallinesilicon on a substrate, further includes a third step for forming alight reflection prevention film on a surface of the formed amorphoussilicon layer, before performing the third step.

Preferably, in the second step, the exposure is carried out by the laserlight having the energy density of approximately 100 mJ/cm² to 230mJ/cm².

Also, preferably, in the second step, the single shot exposure iscarried out by laser light having a duration of approximately 80 ns to200 ns.

Also, according to the present invention there is provided a method ofmanufacturing a MIS transistor, including the following steps of: (a)forming an amorphous silicon layer on a substrate of a metal insulationsilicon transistor; and (b) forming a channel region on the substrate,by exposing laser light, having an energy density of approximately 100mJ/cm² to 500 mJ/cm² and emitted from a laser-light emitting apparatushaving a total energy equal to or greater than 5 J, on the heatedamorphous silicon layer in an extent greater than 10 cm² by single shotexposure to thereby transform the amorphous silicon layer into apolycrystalline silicon thin layer functioning as a channel region ofthe transistor.

Preferably, in the step for forming a channel region, the amorphoussilicon layer is heated at approximately 350° C. to 500° C.

Further, according to the present invention, there is provided a surfacetreatment apparatus comprising: a laser for emitting laser light; anattenuator provided in a first optical path of the laser light emittedfrom the laser; a scanning laser light generating means provided in asecond optical path of the laser light passing through the attenuatorand sweeping the laser light from the attenuator to generate scanninglaser light; a beam homogenizer provided in a third optical path of thescanning laser light from the scanning laser light generating means andhomogenizing the scanning laser light; a chamber provided at a positionirradiated by the laser light passing through the beam homogenizer; and

a stage placing a workpiece therein and provided at a positionirradiated by the laser light incident into the chamber.

Preferably, the laser emits laser light of at least 2 J/pulse or atleast 2 W.

The scanning laser light generating means may comprise: a firstreflection mirror provided in the first optical path of the laser lightpassing through the attenuator; a second reflection mirror provided inthe second optical path of the laser light reflected by the firstreflection mirror; a first rail on which the first reflection mirror ismounted and provided along a line of the x-axial direction as an opticalaxis of the laser light reflected by the first reflection mirror; afirst support which is mounted to reciprocally move with respect to thefirst rail and supports the second reflection mirror and the beamhomogenizer; a second rail which is provided along a line of the y-axialdirection as another optical axis of the laser light reflected by thefirst reflection mirror; and a second support which is mounted toreciprocally move with respect to the second rail and supports the firstrail.

Preferably, the surface treatment apparatus may further comprise a firstdrive unit for causing reciprocal movement of the first support alongthe first rail, and a second drive unit for causing reciprocal movementof the second support along the second rail.

More preferably, a condenser lens, a reticle, and a projection lens maybe provided in the third optical path of the laser light passed the beamhomogenizer. Alternatively, a condenser lens, a reticle, and areflection optical system may be provided in the third optical path ofthe laser light passed through the beam homogenizer.

Preferably, the stage comprises x-axis and y-axis stages movable in twoorthogonal axial directions, an x-axial direction drive unit for drivingthe x-axis stage, and a y-axial direction drive unit for driving they-axis stage.

The surface treatment apparatus may comprise an alignment meansincluding: (a) a length measuring device for determining the positionsof the x-axis and y-axis stages; (b) a target detector for detecting atarget formed on the workpiece on the x-axis and y-axis stages andarranged at a position enabling irradiation of detection light to thetarget; (c) a computation processing unit for performing processing ofcomputations based on a target signal received by the target detectorand instructing the amounts of positional control of the x-axis andy-axis stages; and (d) a drive control unit for instructing the amountsof movement of the x-axis and y-axis stages to the x-axial directiondrive unit and the y-axial direction drive unit based on the amounts ofpositional control instructed from the computation processing unit andthe positions of the x-axis and y-axis stages determined by the lengthmeasuring device.

Alternatively, the surface treatment apparatus may comprise an alignmentmeans, including: (a) a length measuring device for determining theposition of the beam homogenizer; (b) a target detector for detecting atarget formed on the workpiece on the stage and arranged at a positionenabling irradiation of the detection light to the target; (c) acomputation processing unit for performing processing of computationsbased on a target signal received by the target detector and instructingthe amount of positional control of the beam homogenizer; and (d) adrive control unit for instructing the amount of movement of the beamhomogenizer to the first and second drive units based on the amount ofpositional control instructed from the computation processing unit andthe position of the beam homogenizer determined by the length measuringdevice.

Preferably, the surface treatment apparatus further comprise anadjustment means for adjusting laser emission output. The adjustmentmeans includes: (a) a photodetector for detecting the intensity of thelaser light emitted from the laser oscillator; (b) an output controllerfor instructing an intensity of laser light corresponding to the changeof a signal obtained by the photodetector; and (c) a voltage controllerfor receiving instructions from the output controller and controllingthe emission voltage of the laser oscillator.

Alternatively, the adjustment means includes: (a) a photodetector fordetecting the intensity of laser light emitted from the laseroscillator; (b) a controller for instructing an intensity of laser lightcorresponding to the change of a signal obtained by the photodetector;and (c) an attenuator controller for receiving instructions from thecontroller and adjusting the angle of reception of light of theattenuator.

Preferably, the beam homogenizer comprises a fly's eye lens provided inthe third optical path of the laser light, and a condenser lens providedin the third optical path of the laser light passed through the fly'seye lens.

Alternatively, the beam homogenizer comprises a beam expander providedin the third optical path of the laser light, a prism having a planarinner side and having an annular inclined face at the outer peripheryand provided in the third optical path of the laser light passingthrough the beam expander, and a condenser lens for condensing the laserlight split by the prism and provided in the third optical path of thelaser light passed through the prism.

Also, alternatively, the beam homogenizer comprise a beam expanderprovided in the third optical path of the laser light, and a prismhaving a convex conical face and provided in the optical path of thelaser light passed through the beam expander.

More preferably, the surface treatment apparatus may further comprise ashutter blocking the laser light for temporarily opening the opticalpath of the laser light, is provided in the optical path of the laserlight.

According to the present invention, there is further provided a surfacetreatment method, including:

(a) a first step for placing a workpiece on a chamber provided in asurface treatment apparatus, the surface treatment apparatus comprising:a laser oscillator emitting laser light; an attenuator provided in afirst optical path of the laser light emitted from the laser oscillator;a scanning laser light generating means provided in a second opticalpath of the attenuated laser light from the attenuator and sweeping thesame to generate a scanning laser light; a beam homogenizer provided ina third optical path of the scanning laser light and homogenizing thescanning laser light; and a chamber provided at a position to which thehomogenized laser light is exposed, and the workpiece being arranged inthe chamber;

(b) a second step for making the inside of the chamber a predeterminedatmospheric condition; and

(c) a third step for exposing the laser light from the beam homogenizerto the workpiece in the chamber.

Specifically, the second step includes a step for making the inside ofthe chamber an atmospheric condition suitable for to annealing and

wherein the third step includes a step for annealing the workpiece bythe laser light exposure.

More specifically, the second step includes a step for making the insideof the chamber an atmospheric condition suitable for diffusing animpurity into the workpiece, and the third step includes a step forintroducing the impurity contained in the chamber into the workpiece.

Also specifically, the second step includes a step for making the insideof the chamber an atmospheric condition suitable for of oxidization ornitridization and the third step includes a step for forming an oxidelayer or a nitride layer on a surface of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of preferred embodimentswith reference to the accompanying drawings, in which:

FIG. 1 is an explanatory view of the state of irradiation of a laserlight;

FIG. 2 is a view of the relationship between the density of theirradiated energy and the irradiation position;

FIG. 3 is a schematic view of the configuration of an embodiment of asurface treatment apparatus according to the present invention;

FIG. 4 is a view of the partial configuration of the surface treatmentapparatus with a reticle attached;

FIG. 5 is a view of the configuration of the surface treatment apparatuswith a reticle attached;

FIG. 6 is a block diagram of a first alignment means in the surfacetreatment apparatus;

FIG. 7 is a block diagram of a second alignment means in the surfacetreatment apparatus;

FIG. 8 a block diagram of an adjustment means for adjusting the laseremission output, in the surface treatment apparatus;

FIG. 9 is a block diagram of another adjustment means for adjusting thelaser emission output, in the surface treatment apparatus;

FIG. 10 is a schematic view the configuration of a beam homogenizer inFIG. 3;

FIG. 11 is a graph showing the distribution of the intensity of thelaser light in the diametrical direction of the flux by the beamhomogenizer in FIG. 10;

FIG. 12 is a schematic view of the configuration of another beamhomogenizer in FIG. 3;

FIGS. 13A to 13C are graphs showing the distributions of the intensityof the laser light in the diametrical direction of the flux by the beamhomogenizer in FIG. 12;

FIG. 14 is a schematic view of the configuration of still another beamhomogenizer in FIG. 3;

FIGS. 15A and 15B are graphs showing the distributions of the intensityof the laser light in the diametrical direction of the flux, by the beamhomogenizer shown in FIG. 14;

FIG. 16 is a block diagram of the position of installation of a shutterin the surface treatment apparatus;

FIGS. 17A and 17B are views explaining annealing treatment;

FIGS. 18A and 18B are views explaining diffusion of impurities;

FIGS. 19A and 19B are view explaining oxidation treatment;

FIGS. 20A and 20B are process diagrams of the method of forming of apolycrystalline silicon thin film according to an embodiment of thepresent invention;

FIG. 21 is a process diagram of the method of forming a polycrystallinesilicon thin film according to another embodiment of the presentinvention;

FIGS. 22A to 22F are process diagrams of the method of formation of achannel of an MOS transistor according to an embodiment of the presentinvention;

FIGS. 23A to 23E are process diagrams of the method of formation of achannel of an MOS transistor according to another embodiment of thepresent invention;

FIG. 24 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 1 of the present invention;

FIG. 25 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 2 of the present invention;

FIG. 26 is a view of an electron micrograph of the results of TEMobservation (electron diffractograph) of a sample according toComparative Example 1 of the present invention;

FIG. 27 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 3 of the present invention;

FIG. 28 is an electron micrograph showing the results of TEM observation(bright-field image) of a polycrystalline silicon film according toExample 4 of the present invention;

FIG. 29 is a view of an electron micrograph of the results of TEMobservation (electron diffractograph) of a sample according toComparative Example 2 of the present invention; .

FIG. 30 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 5 of the present invention;

FIG. 31 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 6 of the present invention;

FIG. 32 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 7 of the present invention;

FIG. 33 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 8 of the present invention;

FIG. 34 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 9 of the present invention;

FIG. 35 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 10 of the present invention;

FIG. 36 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 11 of the present invention;

FIG. 37 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 12 of the present invention; and

FIG. 38 is a view of an electron micrograph showing the results of TEMobservation (bright-field image) of a polycrystalline silicon filmaccording to Example 13 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the drawings.

SURFACE TREATMENT APPARATUS

An embodiment of a laser light emitting apparatus in accordance with thepresent invention, i.e., a surface treatment apparatus, will bedescribed with reference to the schematic view of the configurationgiven in FIG. 3.

In FIG. 3, a surface treatment apparatus 1 is provided with a laserdevice 11 for emitting laser light 21. The laser device 11 emits laserlight by X-ray excitation and has an energy per pulse of for example atleast 2 J. The laser light 21 is for example emitted in the Gaussianmode.

As the above-mentioned laser device 11, for example, use is made of anexcimer laser for emitting rare gas halide excimer laser light, such asxenon chloride laser light of a wavelength of 308 nm, krypton fluoridelaser light of a wavelength of 249 nm, or argon fluoride light of awavelength of 193 nm. Or, as the laser device 11, use is made of a solidlaser emitting laser light such as YAG (Y₃ Al₅ O₁₂) laser light of awavelength of 1.06 μm, or glass laser light of a wavelength of 1.06 μm,Alexandrite (BeAl₂ O₄) laser light of a wavelength of 0.70 μm to 0.82μm.

Note that when using the higher harmonics of laser light emitted by thelaser device 11, provision is made of a higher harmonic generator (notshown) in the laser device 11. In this case, for example, with a laseremitting YAG laser light (wavelength of 1.06 μm), it is possible toobtain the third harmonics (wavelength of 266 nm).

Further, the above-mentioned laser device 11 may be one which emits thelaser light 21 in pulses or one which emits it continuously. One whichemits pulses, as explained above, is comprised of a laser oscillatorwhich has a pulse energy of at least 2 J. Further, one which emitscontinuously is comprised of a laser oscillator having an output of atleast 2 W.

In a first optical path of the laser light 21 emitted from the laserdevice 11, provision is made of an attenuator 12 through a reflectionmirror 31. The reflection mirror 31 is provided at a position guiding(directing) the laser light 21 to the attenuator 12. The attenuator 12is comprised for example of a quartz substrate on which is formed adielectric thin film. The attenuator 12, further, is provided with arotation drive unit (not shown) able to change the angle of theirradiated face with respect to the incident laser light 21. Thisrotation drive unit is comprised for example of a pulse motor and speedchanger.

In a second optical path of the laser light 21 after passing through theattenuator 12, further, provision is made, through a reflection mirror32, of a laser light scanning means 13 for scanning by the laser light21 in the x- and y-directions. The reflection mirror 32 is provided at aposition guiding (directing) the laser light 21 to the laser lightscanning means 13. The laser light scanning means 13 is provided with afirst reflection mirror 33 and a second reflection mirror 34. The firstreflection mirror 33 is provided in the optical path of the laser light21 after reflected by the reflection mirror 32. The second reflectionmirror 34 is provided in the optical path of the laser light 21 afterreflected by the first reflection mirror 33.

In a third optical path of the laser light 21 emitted from the laserlight scanning means 13, provision is made of a beam homogenizer 14. Thebeam homogenizer 14 converts the mode of the laser light 21 of theGaussian mode emitted from the laser device 11 so that the intensity ofthe laser light in the diametrical direction of the flux becomessubstantially uniform.

The first reflection mirror 33 is provided in the optical path of thelaser light 21 after passing through the attenuator 12 and reflected atthe reflection mirror 32. The second reflection mirror 34 is provided inthe optical path of the laser light 21 after reflected by the firstreflection mirror 33.

Along the optical axis of the laser light 21 reflected by the firstreflection mirror 33, that is, the x-axial direction, provision is madeof a first rail 35 to which the first reflection mirror 33 is attached(mounted). The first rail 35 has attached to it movable back and forth(to reciprocally move) a first support 36 supporting the secondreflection mirror 34 and the above-mentioned beam homogenizer 14.

Along the optical axis of the laser light 21 incident on the firstreflection mirror 33, that is, the y-axial direction, provision is madeof a second rail 37. The second rail 37 has attached to it movable backand forth (to reciprocally move) a second support 38 supporting thefirst rail 35.

Further, a first drive unit 39 connected to the first support 36 througha first drive shaft (not shown) is provided at the end portion of thefirst rail 35. This first drive unit 39 moves the first support 36 backand forth along the first rail 35. Further, a second drive unit 40connected to the second support 38 through a second drive shaft (notshown) is provided at the end portion of the second rail 37 for example.This second drive unit 40 moves the second support 38 back and forthalong the second rail 37.

A chamber 15 is provided in the optical path of the laser light 21 afterpassing through the beam homogenizer 14. Inside the chamber 15, there isprovided a stage 16 on which a workpiece 91 is placed. The stage 16 isprovided with for example a prealignment mechanism (not shown). Thisprealignment mechanism is for making a positioning part formed On theworkpiece 91, for example, an orientation flat or notch of the wafer, bepositioned in a predetermined direction. As the method of positioningusing as a reference the outer shape of the workpiece 91, there is knownthe method of mechanically making the positioning part register with areference part (not shown) formed on the stage 16 and the method ofmaking the positioning part register with a reference part (not shown)formed on the stage 16 using a photodetector.

Further, provision is made of a laser light passage window 41 forpassing the laser light 21 at the side of the chamber 15 irradiated bythe laser light 21. This laser light passage window 41 is comprised forexample of quartz glass. Further, the stage 16 is comprised for exampleof x-axis and y-axis stages movable in the x-axial direction and y-axialdirection by servo motors (not shown). It may also be comprised of fixedstages.

Note that a projection lens (not shown) may be provided in the opticalpath of the laser light 21 between the beam homogenizer 14 and thechamber 15.

The surface treatment apparatus 1 is comprised as explained above.

In the surface treatment apparatus 1 of the above-mentionedconfiguration, the laser light 21 is emitted by the laser device 11 andthe amount of the laser light 21 is adjusted by the attenuator 12.Further, since provision is made of the laser light scanning means 13,the laser light 21 can be made to scan the desired irradiation position.Further, since provision is made of the beam homogenizer 14, theintensity of the laser light in the diametrical direction of the flux ofthe laser light 21 is made substantially uniform. Also, since provisionis made of the chamber 15, the workpiece 91 may be subjected to surfacetreatment by irradiation of the laser light 21 on the workpiece 91placed in a specific atmosphere, for example, a vacuum, oxidizingatmosphere, nitriding atmosphere, atmosphere including diffusionimpurities, etc.

In the laser device 11, the laser light 21 at the time of emission hasan energy of at least 2 J/pulse, so surface treatment of a wide area,for example about 1 cm² or more, by irradiation of a single shot of thelaser light 21 becomes possible. Such surface treatment includes forexample an annealing treatment, diffusion treatment, oxidationtreatment, nitridization treatment, etc.

In the laser light scanning means 13, the first support 36 supportingthe second reflection mirror 34 and the beam homogenizer 14 can be moved(reciprocally) back and forth along the first rail 35 provided in thex-axial direction by, for example, the first drive unit 39. Further, thesecond support 38 supporting the first rail 35 and the first reflectionmirror 33 can be moved back and forth along the second rail 37 providedin the y-axial direction by for example the second drive unit 40.Accordingly, the laser light 21 after passing through the beamhomogenizer 14 may be made to scan anywhere in the x-axial direction andthe y-axial direction.

As shown in FIG. 4, the surface treatment apparatus 1 of theabove-mentioned configuration may be provided with a condenser lens 51,a reticle 52, and a projection lens 53 in the optical path of the laserlight 21 after passing through the beam homogenizer 14.

Note that the condenser lens 51, the reticle 52, and the projection lens53 are provided integral with the beam homogenizer 14 and are movedduring scanning along with the beam homogenizer 14.

In the configuration, by provision of the reticle 52 in the optical pathof the laser light 21 after passing through the beam homogenizer 14, theimage of the reticle is projected on the surface of the workpiece 91.Accordingly, laser light 21 is irradiated only at the desired region ofthe workpiece 91.

As shown in FIG. 5, the surface treatment apparatus 1 of theabove-mentioned configuration may be provided with a condenser lens 54,a reticle 55, and a reflection optical system 56 in the optical path ofthe laser light 21 after passing through the beam homogenizer 14. Thereflection optical system 56 is configured as follows. A reflectionmirror 57 is provided in the optical path of the laser light 21 afterpassing through the condenser lens 54 and the reticle 55. A concavereflection mirror 58 is provided in the optical path of the laser light21 reflected by the reflection mirror 57. Between the reflection mirror57 and the concave surface reflection mirror 58, there is provided aprism 59 for passing the laser light 21 incident from the reflectionmirror 57 side and reflecting the laser light 21 incident from theconcave reflection mirror 58.

With the provision of such a reflection optical system 56, the laserlight 21 is made to scan the workpiece 91 by movement of the stage 16.Further, the beam homogenizer 14 may be integrally provided with thecondenser lens 54, the reticle 55, and the reflection optical system 56and these moved during scanning along with the beam homogenizer 14.

Since the reticle 55 is provided in the optical path of the laser light21 after passing through the beam homogenizer 14, the image of thereticle is projected on the surface of the workpiece 91. Therefore, thelaser light 21 is irradiated only on the desired region of the workpiece91. Further, by providing the reflection optical system 56, thechromatic aberration is decreased compared with the case of provision ofthe condenser lens (54).

Next, an explanation will be made, using the block diagram of FIG. 6, ofan alignment means for detecting the target formed on the workpiece 91and performing positional control. Note that components similar to thoseexplained with reference to the above-mentioned FIG. 3 to FIG. 5 aregiven the same reference numerals.

In FIG. 6, the stage 16 is comprised of an x-axis stage 16x, a y-axisstage 16y, an x-axial direction drive unit 17x provided at the x-axisstage 16x, and a y-axial direction drive unit 17y provided at the y-axisstage 16y.

The x-axis stage 16x can move back and forth in the x-axial direction,while the y-axis stage 16y can move back and forth in the y-axialdirection orthogonal to the x-axis. Further, the x-axial direction driveunit 17x drives the x-axis stage 16x in the x-axial direction, while they-axial direction drive unit 17y drives the y-axis stage 16y in they-axial direction. The x-axial direction drive unit 17x and the y-axialdirection drive unit 17y are comprised for example of DC servo motorsable to perform step drive.

Further, provision is made of a length measuring device 111 fordetermining the positions of the x-axis and y-axis stages 16x and 16y.The length measuring device 111 is comprised for example of a lengthmeasuring device using helium (He)--neon (Ne) laser light.

Further, provision is made of a target detector 112 for detecting atarget 95 of the workpiece 91 placed on the stage 16. The targetdetector 112 is arranged at a position where the target 95 can beirradiated by the detection light 22, for example, between the beamhomogenizer 14 and the workpiece 91. The target detector 112 is forexample comprised of a lighting unit 113 for receiving the detectionlight 22, a detection optical system 114, a photoelectric converter 115,and a target signal detection unit 116.

Note that in the configuration, the laser light 21 irradiated from thebeam homogenizer 14 passes through the prism 114a of the detectionoptical system 114 to be irradiated on the workpiece 91.

The target signal detector 116 of the target detector 112 has connectedto it a processor 117. The processor 117 calculates the amount ofpositional control of the stage 16 by processing of computations basedon the target signal received by the target detector 112.

The processor 117 has connected to it a drive control unit 118. Thedrive control unit 118 receives the signal of the amount of positionalcontrol calculated by the processor 117 and further receives thepositional information of the stage 16 determined by the lengthmeasuring device 111. Further, it calculates the amount of movement ofthe x-axis and y-axis stages 16x and 16y based on the amount ofpositional control and the positional information and instructs theamounts of movement to the x-axial direction drive unit 17x and they-axial direction drive unit 17y.

As explained above, the first alignment means 101 is comprised of thelength measuring device 111, the target detector 112, the processor 117,and the drive control unit 118.

Next, an explanation will be made, using the block diagram of FIG. 7, ofan alignment means for detecting a target formed on the workpiece 91 andperforming positional control of the beam homogenizer 14. Note thatcomponents similar to those explained with reference to the FIG. 3 toFIG. 6 are given the same reference numerals.

In FIG. 7, provision is made of a length measuring device 119 fordetermining the position of the beam homogenizer 14 in the x-axialdirection and the y-axial direction. The length measuring device 119 iscomprised for example of a length measuring device using helium-neon(He--Ne) laser light.

Further, provision is made of a target detector 112 for detecting atarget 95 of the workpiece 91 placed on the stage 16. The targetdetector 112 is arranged at a position where the target 95 can beirradiated by the detection light 22, for example, between the beamhomogenizer 14 and the workpiece 91. The target detector 112 has asimilar configuration as that explained in the FIG. 6.

Note that in the above-mentioned configuration, the laser light 21irradiated from the beam homogenizer 14 passes through the prism 114a ofthe detection optical system 114 to be irradiated on the workpiece 91.

The target signal detector 116 of the target detector 112 has connectedto it a processor 117. The processor 117 calculates the amount ofpositional control of the beam homogenizer 14 by processing ofcomputations based on the target signal received by the target detector112.

The processor 117 has connected to it a drive control unit 118. Thedrive control unit 118 receives the signal of the amount of positionalcontrol calculated by the processor 117 and further receives thepositional information of the beam homogenizer 14 determined by thelength measuring device 119. Further, it calculates the amount ofmovement of the beam homogenizer 14 based on the amount of positionalcontrol and the positional information and instructs the amounts ofmovement to the first and second drive units 39 and 40.

The first and second drive units 39 and 40 are comprised for example ofDC servo motors able to perform step drive.

As explained above, the second alignment means 102 is comprised by thelength measuring device 119, the target detector 112, the processor 117,and the drive control unit 118.

Note that in the surface treatment apparatus 1 provided with the secondalignment means 102, the stage 16 may also be a fixed stage.

It is also possible to provide the first alignment means 101 explainedwith reference to FIG. 6 and the second alignment means 102 explainedwith reference to FIG. 7. In this case, for example, the secondalignment means 102 performs prealignment at the micron level and forexample the first alignment means 101 performs fine alignment at thesubmicron level.

As mentioned above, since the surface treatment apparatus 1 is providedwith the first alignment means 101 and/or the second alignment means102, positioning at the submicron level becomes possible. As a result,annealing treatment at a submicron order of positioning accuracy can beperformed by the step and repeat method.

Further, in the first and second alignment means 101 and 102 explainedabove, for example it is possible to use an alignment target used in thephotosensitizing step of lithographic processes. In this case, there isno need for newly forming a target exclusively for the annealingtreatment. Further, by combining a target (not shown) formed on thereticle 52 (55) (see FIG. 4 (FIG. 5)) and the target 95 formed on theworkpiece 91, it becomes possible to align the reticle image at thesubmicron level. As a result, annealing treatment for transferring thereticle image with a submicron order of positioning accuracy can beperformed by the step and repeat method.

The alignment means explained above was just one example and may be ofany configuration so long as it is provided with a target detector fordetecting the target 95 formed on the workpiece 91 and is a controlmeans for driving the stage 16 or a control means for driving the beamhomogenizer 14 so that the position of irradiation of the laser light 21irradiated from the beam homogenizer 14 is made to register with theregion of the workpiece 91 for the annealing treatment.

Next, an explanation will be made, with reference to the block diagramof FIG. 8, of an example of the means for adjusting the emission outputof the above-mentioned laser device 11.

In FIG. 8, the surface treatment apparatus 1 is provided with anadjustment means 61 for adjusting the laser emission output. Theadjustment means 61 for adjusting the laser emission output is comprisedof a photodetector 62, an output controller 63, and a voltage controller64.

The photodetector 62 detects the intensity of the laser light 21 and isfor example comprised of a device for converting the laser light 21 to acurrent or voltage. For example, it is comprised of a photodiode, aphotoelectric electron multiplier tube, or a photocell. Further, forexample, it is provided in the optical path of the laser light 21 afterreflected by the attenuator 12.

The output controller 63 is connected to the photodetector 62 andinstructs an emission voltage value so as to maintain constant theintensity of the laser light 21 emitted from the laser device 11 inaccordance with the change in the signal obtained by the photodetector62.

Further, the voltage adjuster 64 is connected to the output controller63 and adjusts the high voltage applied to the laser device 11 uponreceipt of an instruction from the output controller 63. It is forexample comprised of a variable resistor.

In the adjustment means 61 for adjusting the laser emission output, theoutput controller 63 instructs the intensity of emission of the laserlight 21 based on the intensity of the laser light 21 received by thephotodetector 62 and, receiving that instruction, the voltage controller64 adjusts the emission voltage of the laser device 11, so the laserlight 21 is emitted by a stable output from the laser device 11.

Next, an explanation will be made, with reference to the block diagramof FIG. 9, of another adjustment means 65 for adjusting the emissionoutput of a configuration other than the adjustment means (61) foradjusting the laser emission output of the above configuration.

The means 65 for adjusting the laser emission output is comprised of aphotodetector 66, a controller 67, and an attenuator controller 68.

The photodetector 66 is one which detects the intensity of the laserlight 21 and is for example comprised of a device which converts thelaser light 21 to a current or voltage. For example, it is comprised ofa photodiode, a photoelectric electron multipler tube, or a photocell.Further, for example, the reflection mirror 31 may be formed by asemitransmission mirror and the photodetector 66 may be provided in theoptical path of the laser light 21 after passing through this reflectionmirror 31. The photodetector 66 is for example comprised of a photodiodewhich can detect the laser light 21. The controller 67 is connected tothe photodetector 66 and instructs the intensity of the laser light 21in accordance with the change of the signal obtained by thephotodetector 66. Further, the attenuator controller 68 adjusts theangle of reception of light of the attenuator 12 with respect to thedirection of incidence of the laser light 21 based on the instructionfrom the controller 67 and is for example comprised of a pulse motor.

With the adjustment means 65 for adjusting the laser emission output,the angle of the attenuator 12 is instructed by the controller 67 basedon the intensity of the laser light 21 received by the photodetector 66.Receiving this instruction, the attenuator controller 68 adjusts theangle of reception of light of the attenuator 12 with respect to thedirection of incidence of the laser light 21. Accordingly, even if thelaser light 21 emitted from the laser device 11 is unstable in output,the laser light 21 after passing through the attenuator 12 is stabilizedin output.

Next, three examples of the configuration of the above-mentioned beamhomogenizer 14 will be described with reference to FIG. 10 to FIGS. 15Aand 15B.

As shown in FIG. 10, a beam homogenizer 14A (14) as a first example iscomprised of a fly's eye lens 71 provided in the optical path of thelaser light 21 and a condenser lens 72 provided in the optical path ofthe laser light 21 after passing through it. With the beam homogenizer14A, the intensity of the laser light in the diametrical direction ofthe flux of the laser light 21 is distributed to input substantiallyuniformly to the condenser lens 71 by the fly's eye lens 71. Further, asshown in FIG. 11, the incident laser light 21 to the condenser lens 72is made uniform parallel light by the condenser lens 72.

Next, an explanation will be made of a second example of a beamhomogenizer with reference to the schematic view of the configurationgiven in FIG. 12.

As shown in FIG. 12, a beam homogenizer 14B (14) is comprised of a beamexpander 73, a prism 74, and a condenser lens 75 provided in the opticalpath of the laser light 21. The beam expander 73 is comprised of a lensor a group of lenses of constructions for expanding the diameter of theflux of the laser light 21. For example, it is comprised of a concavecylindrical lens 73A and a convex cylindrical lens 73B. The prism 74 hasa center portion formed as a flat plane and an outer peripheral portionformed as an inclined face so as to form part of a conical face. Thecondenser lens 75 is comprised of a lens of a construction whichcondenses the laser light 21 split by the prism 74 to form a flux of asubstantially uniform light intensity at the surface of the workpiece91.

Note that the prism 74 may be formed in an annular shape and the face ofthe annular portion may be given a slant so as to form part of theconical face. In the case of this configuration, a reflection preventingfilm may be formed at the inside of the annular portion.

In the beam homogenizer 14B, the diameter of the flux of the laser light21 is expanded by the beam expander 73. As shown by FIG. 13A, theincident laser light 21 is split by the prism 74 into a center flux 21a(21) and an outer periphery flux 21b (21). Next, as shown in FIG. 13B,the outer periphery flux 21b is inverted at the outer periphery of thecenter flux 21a and made incident on the condenser lens 75 along withthe center flux 21a. Further, as shown in FIG. 13C, the inverted outerperiphery flux 21b is superposed on the side periphery of the centerflux 21a to form a flux of a uniform energy density (21).

Next, an explanation will be made of a third example of the beamhomogenizer with reference to the schematic configuration shown in FIG.14.

A beam homogenizer 14C (14) is comprised of a beam expander 76 and prism77 provided in the optical path of the laser light 21. The beam expander76 is for example comprised of a concave cylindrical lens 76A and aconvex cylindrical lens 76B. The prism 77 is comprised of a lens with atleast one face formed as a convex conical face.

Note that with the beam homogenizer 14 of the above-mentionedconfiguration, the workpiece 91 is set at a position where the intensityof laser light at the diametrical direction of the flux becomessubstantially uniform.

With the beam homogenizer 14C, the diameter of the flux of the laserlight 21 is expanded by the beam expander 76. As shown in FIG. 15A, theincident laser light 21 is split by the prism 77 to be symmetrical inthe radial direction about the optical axis. Inversion is performed andthe results superposed to give, as shown in FIG. 15B, laser light 21with a substantially uniform intensity of laser light in the diametricaldirection of the flux.

Next, an explanation will be made of an example of provision of ashutter in the optical path of the laser light 21 in the surfacetreatment apparatus 1 mentioned above with reference to a block diagramof the position of installation in FIG. 16.

A shutter 81, for example, is provided between the laser device 11 andthe reflection mirror 31. The shutter 81 is comprised of a shutter whichblocks the laser light 21 and which therefore can temporarily open theoptical path of the laser light 21. For example, it is comprised of afocal plane shutter formed of a material which will not undergo anychange even if irradiated by laser light 21.

Note that the shutter 81 may be any configuration of shutter so long asit has durability with respect to the laser light 21 irradiated at thetime the shutter 81 is closed.

Further, as explained above, the mounting position of the shutter 81 maybe in the optical path of the laser light 21 from the reflection mirror31 to the chamber 15 except between the laser device 11 and thereflection mirror 31.

The shutter 81 blocks the optical path of the laser and temporarilyopens the optical path of the laser light 21 in accordance with need, soit is possible to take out a single pulse from the continuously emittedpulses of laser light 21. Accordingly, laser light can be continuouslyemitted in pulses from the laser device 11 and the output per pulse canbe stabilized. The shutter is operated to open and close the opticalpath in synchronization with the emission of the laser light 21 from thelaser device 11 in this state. Due to this, it is possible to take outstably emitted pulses of laser light 21. Further, when the laser light21 is continuously emitted from the laser device 11, laser light 21substantially the same as pulse emission can be obtained by opening andclosing the shutter 81.

Next, an explanation will be made, with reference to FIGS. 17A and 17B,of the method of annealing treatment using a surface treatment apparatus1 of the above configuration.

As shown in FIG. 17A, at a first step, the workpiece 91 is placed on thestage 16 provided at the inside of the chamber 15. Next, the atmosphereinside the chamber 15 is for example made a vacuum to establish theannealing treatment atmosphere. Next, as shown in FIG. 17B, theworkpiece 91 is irradiated with the laser light 21 to anneal theworkpiece 91. At this time, the laser light 21 emitted from the laserdevice 11 has an energy of about 2 J/pulse or more. Accordingly, even ifthe intermediate loss up to the irradiation of the workpiece 91 is 30percent, the surface of the workpiece 91 is irradiated with an energy of1.4 J/pulse or more.

In annealing treatment for activating a source-drain region of an MOSthin film transistor, for example, an energy density of about 0.3 J/cm²is required. Accordingly, with laser light 21 of 1.4 J/pulse, it ispossible to perform annealing treatment of an area of about 4.6 cm²(about 2.1 cm×2.1 cm) by irradiation of a single pulse of laser light.

For example, when using the laser device 11 which generates laser light21 having an energy of about 10 J/pulse, assuming in the same way asabove an intermediate loss of 30 percent, it is possible to performannealing treatment by irradiation of a single pulse of laser light onan area of about 23 cm² (about 4.8 cm×4.8 cm).

In this way, in the above surface treatment method, it is possible toirradiate a wide area (for example about 1 cm² or more) by a single shotof laser light 21, so a wide area of the surface of the workpiece 9 isannealed.

Next, an explanation will be made, with reference to FIGS. 18A and 18B,of the method of impurity diffusion treatment using the surfacetreatment apparatus 1 of the above-mentioned configuration.

As shown by FIG. 18A, in a first step, the workpiece 91 is placed on thestage 16 provided at the inside of the chamber 15. Next, the inside ofthe chamber 15 is made an atmosphere for performing the impuritydiffusion treatment, e.g., one in which a gaseous mixture of diborane(B₂ H₆) and argon (Ar) is set to 26.7 Pa. Next, as shown in FIG. 18B,the workpiece 91 is irradiated by laser light 21 to diffuse the impurityin the atmosphere, for example, the boron, in the workpiece 91. Thisforms the diffusion layer 92. At this time, the laser light 21 emittedfrom the laser device 11 has an energy of about 2 J/pulse or more.Accordingly, even if the intermediate loss up to the irradiation of theworkpiece 91 is 30 percent, the surface of the workpiece 91 isirradiated with an energy of 1.4 J/pulse or more.

When an energy density of about 1.0 J/cm² is required, it is possible touse laser light 21 of 1.44 J/pulse to perform impurity diffusiontreatment on an area of 1.44 cm² (about 1.2 cm×1.2 cm) by irradiation ofa single pulse of laser light.

When using the laser device 11 which emits laser light 21 having anenergy of about 10 J/pulse, assuming in the same way as above anintermediate loss of 30 percent, it is possible to perform impuritydiffusion treatment by irradiation of a single pulse of laser light onan area of about 14 cm² (about 3.7 cm×3.7 cm).

The depth of diffusion (concentration) becomes greater along with thenumber of pulses.

In such an impurity diffusion treatment method, it becomes possible toirradiate a wide area, for example about 1 cm² or more, and introduceand diffuse an impurity into the region of the surface of the workpiece91 irradiated by the laser light 21.

Next, an explanation will be made, with reference to FIGS. 19A and 19B,of the method of oxidation treatment, or nitridization treatment, usingthe surface treatment apparatus 1 of the above-mentioned configuration.

In FIG. 19A, at the first step, the workpiece 91 is mounted on the stage16 provided inside the chamber 15. Next, the inside of the chamber 15 ismade an oxidizing atmosphere or nitriding atmosphere. In the case of anoxidizing atmosphere, the atmosphere is made one including oxygen forexample. Further, in the case of a nitriding atmosphere, the atmosphereis made one including nitrous oxide (N₂ O) or ammonia (NH₃) for example.

Next, as shown in FIG. 19B, the laser light 21 is irradiated on theworkpiece 91 to oxidize (or nitridize) the surface layer of theworkpiece 91 with the oxygen (or nitrogen) in the atmosphere and form anoxide layer (or nitride layer) 93.

At this time, the laser light 21 emitted from the laser device 11 has anenergy of about 2 J/pulse or more. Accordingly, even if the intermediateloss up to irradiation of the workpiece 91 is 30 percent, the surface ofthe workpiece 91 is irradiated with an energy of about 1.4 J/pulse ormore.

In the oxidation treatment, when for example an energy density of about1.0 J/cm² is required, an oxide layer 92 may be formed by irradiation ofa single pulse of laser light on an area of about 1.44 cm² (about 1.2cm×1.2 cm) using laser light 21 of 1.4 J/pulse.

When using the laser device 11 which generates the laser light 21 havingan energy of about 10 J/pulse, assuming in the same way as above anintermediate loss of 30 percent, an oxide layer 93 may be formed byirradiation of a single pulse of laser light on an area of about 14 cm²(about 3.7 cm×3.7 cm).

Further, it is possible to perform nitridization treatment underconditions substantially the same as the above.

By making the inside of the chamber an oxidizing atmosphere, ornitriding atmosphere, and irradiating laser light on a wide area of theworkpiece, an oxide layer or nitride layer may be formed on the surfacelayer of the region of the workpiece irradiated by the laser light.

In this oxidation or nitridization treatment method, it is possible toirradiate a wide area, for example, one of about 1 cm² or more, with asingle shot of the laser light 21, so the region of the workpiece 91irradiated by the laser light 21 may be oxidized or nitrided.

As explained above, according to the surface treatment apparatus of thepresent invention, since provision is made of a laser light scanningmeans, it is possible to scan a desired irradiation position with laserlight. Further, since the chamber is provided, it is possible to performvarious types of surface treatment by setting the workpiece in aspecific atmosphere, for example, a vacuum, oxidizing atmosphere,nitriding atmosphere, atmosphere including a diffusion impurity, etc.,and then irradiating it with laser light.

The laser mounted in the above-mentioned surface treatment apparatus hasan output of at least 2 J/pulse, so it is possible to perform surfacetreatment on a wide area, for example, about 1 cm² or more, byirradiation of a single shot of laser light. Further, the energy densityof the laser light in the irradiated region can be made substantiallyuniform.

With the above-mentioned laser light scanning means, the first supportsupporting the second reflection mirror and the beam homogenizer becomesmovable back and forth (reciprocally movement) along the first rail andthe second support supporting the first rail and first reflection mirrorbecomes movable back and forth along the second rail, so the laser lightafter passing through the beam homogenizer can be used to freely scan inthe x-axial and y-axial directions.

With the configuration in which the reticle is provided in the surfacetreatment apparatus, it is possible to project the image of the reticleon the surface of the workpiece, so it is possible to irradiate laserlight on a desired region of the workpiece.

With the configuration in which the alignment means is provided in thesurface treatment apparatus, it is possible to position the irradiationposition of the laser light to the workpiece at the level of severalmicrons or submicrons. As a result, it becomes possible to perform theannealing treatment while setting the annealing treatment position witha high precision.

With the adjustment means for adjusting the laser emission outputprovided in the surface treatment apparatus, the voltage applied by thelaser is adjusted by the voltage controller based on the intensity ofthe laser light received by the photodetector, so emission of laserlight with a fixed output is possible.

With the another adjustment means for adjusting the laser emissionoutput provided in the surface treatment apparatus, the angle ofreception of light of the attenuator is adjusted by the attenuatorcontroller based on the intensity of the laser light received by thephotodetector, so it is possible to stabilize the output of the laserlight after passing through the attenuator.

With the beam homogenizer provided in the surface treatment apparatus,it is possible to obtain laser light with a substantially uniform laserlight intensity in the diametrical direction of the flux of the laserlight by the fly's eye lens.

With the beam homogenizer provided with the prism having an annularconical face, the laser light may be split by the prism into a centerflux and an outer periphery flux, the outer periphery flux may beinverted and moved to the side periphery of the center flux, and theflux moved to the side periphery may be condensed at the side peripheryof the center flux by the condenser lens, so it is possible to obtainlaser light with a substantially uniform laser light intensity in thediametrical direction of the condensed flux.

With the beam homogenizer provided with the prism having a convexconical face, the laser light may be split by the prism into a centerflux and an outer periphery flux, the outer periphery flux may beinverted and superposed at the side periphery of the center flux, andtherefore it is possible to obtain laser light with a substantiallyuniform laser light intensity in the diametrical direction of thecondensed flux.

By provision of a shutter in the surface treatment apparatus, it ispossible to cause the continuous emission of pulses of laser light,stabilize the same, and then take out a stabilized pulse. Therefore, itis possible to stabilize the density of irradiated energy of the laserlight irradiated on the workpiece.

In the surface treatment method of the present invention, use is made ofthe surface treatment apparatus, so the laser output per shot is largeand it becomes possible to treat the surface of a wide area by a singleshot. Further, if use is made of a short wavelength laser light, itbecomes possible to anneal only a shallow region of the workpiece.Alternatively, it becomes possible to perform impurity diffusiontreatment for diffusing an impurity in a workpiece, an oxidizingtreatment for forming an oxide layer, or a nitriding treatment forforming a nitride layer.

FORMATION OF POLYCRYSTALLINE SILICON LAYER

Note, a method of forming a thin layer (thin film) of polycrystallinesilicon on a substrate will be described.

First Embodiment

A first embodiment of a method of forming a polycrystalline silicon thinfilm of the present invention will be explained by a process diagram ofthe formation of a polycrystalline silicon thin film shown in FIG. 1.

As shown in FIG. 20A, an insulating layer 212 is formed on the top layerof a substrate 211. The substrate 211 is not particularly limited, butfor example use may be made of a silicon substrate or othersemiconductor substrate or a glass substrate etc. The insulating layer212 is not particularly limited, but for example use may be made ofsilicon oxide. Next, as the first step, for example, use is made of thechemical vapor deposition method to deposit an amorphous silicon layer213 on the insulating layer 212. This amorphous silicon layer 213 isdeposited to a thickness of for example 40 nm.

The amorphous silicon layer 213 is formed for example by the lowpressure (LP) CVD method using monosilane (SiH₄). As the temperaturecondition of the deposition, the temperature is preferably set to lessthan 500° C. for example. By setting the deposition temperature to lessthan 500° C. in this way, it is possible at the next step to form apolycrystalline silicon thin film with few crystal defects in the grainsat the time of annealing the amorphous silicon layer 213 by an excimerlaser light emitted from, for example, the surface treatment apparatusmentioned above. Note that when the above-mentioned depositiontemperature is set to a temperature higher than 550° C., the crystalspartially grow and a polycrystalline silicon thin film with a highdefect density is formed.

Next, at least the amorphous silicon layer 213 is heated along with thesubstrate (substrate heating). This substrate heating is performed usingfor example a resistance wire. The substrate heating temperature is setto 400° C. for example.

Next, as shown in FIG. 20B, the amorphous silicon layer 213 isirradiated with excimer laser light 15 for direct annealing of theamorphous silicon layer 213. The melted region is recrystallized and apolycrystalline silicon thin film 213a is formed.

As the excimer laser light 215, use is made for example of xenonchloride (XeCl) excimer laser light of a wavelength of 308 nm. In thiscase, use is made for example of the above-mentioned surface treatmentapparatus with a total energy of the excimer laser light 215 of at least10 J, the excimer laser energy density is set to for example 300 mJ/cm²,and the pulse width is set to for example 150 ns for the irradiation.

Note that the excimer laser light may be any laser light so long as itis of a wavelength which can be easily absorbed by the amorphous siliconlayer 213. For example, use may be made of krypton fluoride (KrF)excimer laser light of a wavelength of 249 nm, argon fluoride (ArF)excimer laser light of a wavelength of 193 nm, etc. In this case, thevalue of the density of the irradiated energy is suitably selected.

In the method of forming a polycrystalline silicon thin film accordingto this embodiment, by using an excimer laser, provided in the abovementioned surface treatment apparatus, with a total energy of at least10 J and setting the thickness of the amorphous silicon layer, thesubstrate heating temperature, the pulse width of the excimer laserlight, and the energy density of the excimer laser light to specificvalues, it is possible to form a polycrystalline silicon thin film 213awith an average grain size of 150 nm and a low electron trap density atthe grain boundaries and in the grains over a wide region of at least 6cm×6 cm (36 cm²). Accordingly, if the obtained polycrystalline siliconthin film is used for a medium or small sized direct-view type liquidcrystal display etc., mass production of high performance liquid crystaldisplays becomes possible.

Second Embodiment

Next, an explanation will be made, using the process diagram of FIG. 21,of the method for depositing a light reflection prevention film 214 onthe amorphous silicon layer 213 and irradiating this with excimer laserlight 215 as a second embodiment of the method of forming apolycrystalline silicon thin film.

In the process shown in FIG. 21, the amorphous silicon layer 213 isformed on the surface of the substrate 211 in a similar way to the firstembodiment, then a light reflection prevention film 214 is deposited tofor example 50 nm on the amorphous silicon layer 213. The conditions forformation of the amorphous silicon layer 13 etc. are similar to those inthe first embodiment.

As the light reflection prevention film 214, use may be made of forexample silicon oxide (Si_(x) O_(y)), Si_(x) N_(y), or Si_(x) O_(y) N₂.The thickness of the light reflection prevention film 214 is determinedso as to give the maximum reflection prevention effect.

In the case of this embodiment, use is made for example of theabove-mentioned surface treatment apparatus with a total energy of theexcimer laser light 215 of at least 10 J, the energy density is set tofor example 200 mJ/cm², and the pulse width is set to for example 150 nsfor the irradiation. Next, an etching technique is used to remove thelight reflection prevention film 214. In the method of formation of thepolycrystalline silicon thin film according to this second embodiment,by using the light reflection prevention film 214, it is possible toobtain a polycrystalline silicon thin film 213b similar to thepolycrystalline silicon thin film 213a obtained in the first embodimentwith the excimer laser energy density lower than that in the firstembodiment.

If the method of formation of a polycrystalline silicon thin filmaccording to the present invention is used, the polycrystalline siliconthin film 213b with an average grain size of 150 nm and a low electrontrap density at the grain boundaries and in the grains can be obtainedover a wide region of at least 6 cm×6 cm by a single annealingtreatment. Accordingly, if the obtained polycrystalline silicon thinfilm is used for a medium or small sized direct-view type liquid crystaldisplay etc., mass production of high performance liquid crystaldisplays becomes possible.

Third Embodiment

Next, an explanation will be made, with reference to the manufacturingprocess diagram of FIGS. 22A to 22F, of the method of production of abottom gate type MIS transistor (TFT: thin film transistor) having achannel region formed in the polycrystalline silicon thin film formedusing the method of formation of a polycrystalline silicon thin filmaccording to the above-mentioned first embodiment and second embodiment.Note that components similar to those explained with reference to theabove-mentioned first embodiment and second embodiment are given thesame references and explanations thereof are partially omitted.

First, as shown in FIG. 22A, for example, the chemical vapor depositionmethod is used to form an insulating layer 212 on the substrate 211.Next, a gate electrode formation film 220 is deposited on the insulatinglayer 212. The gate electrode formation film 220 is for example formedby the CVD method, is comprised of a polycrystalline or amorphoussilicon doped with phosphorus, and for example has a thickness of 100nm.

Next, a photolithographic technique and etching are used to remove theportion of the gate electrode formation film 220 shown by the two-dotline and to form a gate electrode 221 by the remaining gate electrodeformation film 220.

Next, for example, the chemical vapor deposition method (or the heatoxidation method etc.) is used to form a gate insulating film 222 in astate covering at least the surface of the above-mentioned gateelectrode 221. The gate insulating film 222 is comprised for example ofsilicon oxide and has a thickness of for example 30 nm.

Next, as shown in FIG. 22B, a method similar to the one explained in theabove-mentioned first embodiment or second embodiment is used todeposit, by the chemical vapor deposition method, able to form a filmsuperior in step coverage, an amorphous silicon layer 223 on the surfaceof the gate insulating film 222. This amorphous silicon layer 223 isformed for example to a thickness of 40 nm.

Next, as shown in FIG. 22C, excimer laser light 225 is irradiated on theamorphous silicon layer 223 under conditions similar to theabove-mentioned first embodiment or second embodiment to perform directannealing of the amorphous silicon layer 223. The melted region isrecrystallized to form the polycrystalline silicon thin film 223a.

As the excimer laser light 225, use is made for example of xenonchloride (XeCl) excimer laser light of a wavelength of 308 nm. In thiscase, use is made of the surface treatment apparatus mentioned above ofa total energy of the excimer laser light 225 of for example at least 10J, the excimer laser energy density is set to for example 300 mJ/cm²,and the pulse width is set to for example 150 ns for the irradiation.

Next, as shown in FIG. 22D, for example, a lithographic technique andetching technique are used to remove the interlayer portion 226 in thepolycrystalline silicon thin film 223a shown by the two-dot chain lineand form a conductive layer formation region 227 of a predeterminedpattern by the polycrystalline silicon thin film 223a on the gateelectrode 221 and at the two sides of the same.

Next, as shown in FIG. 22E, a coating technique and lithographictechnique are used to form an ion implantation mask 228 comprised of,for example, a resist film, by the pattern of the gate electrode 221 onthe above-mentioned conductive layer formation region 227.

The ion implantation method is then used to introduce an impurity (notshown) into the conductive layer formation region 227 at the two sidesof the above-mentioned gate electrode 221 and form the source-drainregions 229 and 230. The conductive layer formation region 227 beneaththe ion implantation mask 231 becomes the channel region 231 of the TFTtype MOS transistor.

As the ion implantation conditions at this time, for example, theimplantation energy is set to 10 KeV, the dosage is set to 3×10¹⁵ cm⁻²,and boron ions (B⁺) are introduced. Alternatively, the implantationenergy is set to 35 KeV, the dosage is set to 3×10¹⁵ cm⁻², andborofluoride ions (BF₂ ⁺) are introduced.

Next, washer treatment or wet etching etc. is used to remove the ionimplantation mask 228.

Annealing for activating the source-drain regions 229 and 230 is thenperformed. As the annealing conditions, for example, the annealingtreatment temperature is set to 900° C. and the annealing treatment timeis set to 20 minutes.

Next, as shown in FIG. 22F, an interlayer insulating film 232 is formedso as to cover the conductive layer formation region 227. The interlayerinsulating film 232 is not particularly limited, but for example may bea film formed by the CVD method such as a silicon oxide film, siliconnitride film, PSG (phosphosilicate glass) film, or BPSG(borophosphosilicate glass) film.

Next, the usual photolithographic technique and etching technique areused to form the contact holes 234 and 235 in the interlayer insulatingfilm 232. Further, electrodes 236 and 237 connecting to the source-drainregions 229 and 230 through the contact holes 234 and 235 are formed.Further, while not shown, an electrode connected to the gate electrode221 is also formed. These electrodes are comprised of polycrystallinesilicon or aluminum or another metal. After this, sintering treatment ofthe electrodes is performed. The conditions for the sintering treatmentare not particularly limited, but for example may be 400° C. and onehour.

A bottom gate type of MOS transistor 240 is formed in this way.

In the method for formation of a bottom gate type MOS transistor 240,substantially the same procedure is followed as with the method offormation of a polycrystalline silicon thin film explained withreference to the above-mentioned first embodiment or second embodimentto form the polycrystalline silicon thin film 223a, and thepolycrystalline silicon thin film 223a is used as the conductive layerformation region 227. By forming a channel region 231 there, it becomespossible to obtain a channel region 249 with a small electron trapdensity at the grain boundaries and in the grains. As a result, a TFTtype MOS transistor with superior electrical characteristics isobtained.

When the bottom gate construction TFT type MOS transistor 240 accordingto this embodiment is used for an SRAM load device, for example, thepower consumption of the SRAM is reduced. Further, the resistance of theSRAM to software errors is improved, so the reliability is improved.Further, the TFT type MOS transistor according to the present embodimentmay be suitably used for a drive transistor of a liquid crystal displayas well.

Fourth Embodiment

Next, an explanation will be made, with reference to the manufacturingprocess diagrams of FIGS. 23A to 23E, of the method of production of atop gate type MOS transistor (TFT) having a channel region formed in thepolycrystalline silicon thin film formed using the method of formationof a polycrystalline silicon thin film according to the above-mentionedfirst embodiment and second embodiment. Note that components similar tothose explained with reference to the above-mentioned first embodimentand second embodiment are given the same references and explanationsthereof are partially omitted.

First, as shown in FIG. 23A, for example, the chemical vapor depositionmethod is used to form the insulating layer 212 on the substrate 211.Next, a method similar to the one explained in the above-mentioned firstembodiment or second embodiment is used to deposit, by the chemicalvapor deposition method, able to form a film superior in step coverage,an amorphous silicon layer 241 on the surface of the insulating layer212. This amorphous silicon layer 241 is formed for example to athickness of 40 nm.

Next, the excimer laser light is irradiated on the amorphous siliconlayer 241 under conditions similar to the above-mentioned firstembodiment or second embodiment to perform direct annealing of theamorphous silicon layer 241. The melted region is recrystallized to formthe polycrystalline silicon thin film 241a.

As the excimer laser, use is made for example of xenon chloride (XeCl)excimer laser light of a wavelength of 308 nm. In this case, use is madeof the above mentioned surface treatment apparatus of a total energy ofthe excimer laser light 225 of for example at least 10 J, the excimerlaser energy density is set to for example 300 mJ/cm², and the pulsewidth is set to for example 150 ns for the irradiation.

Next, as shown in FIG. 23B, for example, a lithographic technique andetching technique are used to etch the polycrystalline silicon thin film241a and form a conductive layer formation region 242 of a predeterminedpattern.

Next, for example, the chemical vapor deposition method (CVD) or theheat oxidation method etc. is used to form a gate insulating film 243 onthe surface of the above-mentioned conductive layer formation region242. The gate insulating film 243 is comprised for example of siliconoxide and has a thickness of for example 30 nm.

Further, as shown in FIG. 23C, for example, the CVD method is used todeposit a gate electrode formation film 244 on the surface of theabove-mentioned gate insulating film 243. The gate electrode formationfilm 244 is for example comprised of a polycrystalline or amorphoussilicon doped with phosphorus, and for example has a thickness of 100nm.

Next, a lithographic technique using the resist film 245 and an etchingtechnique are used to remove the above-mentioned gate electrodeformation film 244 at the portion shown by the two-dot chain line and toform the gate electrode 246 by the gate electrode formation film 244located on the conductive layer formation region 242.

Next, as shown in FIG. 23D, the resist film 245 used at the time ofetching for forming the gate electrode 246 is used as an ionimplantation mask and ion implantation is performed. Note that for theion implantation mask, use may also be made of a separate mask from theresist mask 245 of the etching. Due to this ion implantation, animpurity (not shown) is introduced into the above-mentioned conductivelayer formation region 242 positioned at the two sides of the gateelectrode 246 and the source-drain regions 247 and 248 are formed in aself-aligning manner. Accordingly, a channel region 249 is formed in aself-aligning manner at the conductive layer formation region 242comprised of the polycrystalline silicon.

As the ion implantation conditions at that time, for example, theimplantation energy is set to 10 KeV, the dosage is set to 3×10¹⁵ cm⁻²,and boron ions (B⁺) are introduced. Alternatively, the implantationenergy is set to 35 KeV, the dosage is set to 3×10¹⁵ cm⁻², andborofluoride ions (BF₂ ⁺) are introduced.

Next, washer treatment or wet etching etc. is used to remove the resistfilm 245.

Annealing for activating the source-drain regions 247 and 248 is thenperformed. As the annealing conditions, for example, the annealingtreatment temperature is set to 900° C. and the annealing treatment timeis set to 20 minutes.

Next, as shown in FIG. 23E, an interlayer insulating film 250 is formedby the CVD method to a thickness of for example 150 nm to 200 nm on thegate electrode 246 and the gate insulating film 243. The interlayerinsulating film 250 is formed by a PSG film or BPSG film or othersilicon oxide type film or silicon nitride film.

Next, the Usual photolithographic technique and etching are used to formthe contact holes 251, 252, and 253. Further, the usual interconnectionformation techniques are used to form the electrodes 255, 254, and 256connecting to the gate electrode 246 and the source-drain regions 47 and48 through the contact holes 251, 252, and 253. The electrodes arecomprised of polycrystalline silicon or aluminum or another metal.

After this, sintering is performed. The conditions for the sinteringtreatment are not particularly limited, but for example may be 400° C.and one hour.

A top gate type of MOS transistor 260 is formed in this way.

In the method for formation of a top gate type MOS transistor 260according to this embodiment, by using the method of formation of apolycrystalline silicon thin film according to the above-mentioned firstembodiment or second embodiment to form the polycrystalline silicon thinfilm 241a and by forming a channel region 249 in the polycrystallinesilicon thin film 241a, it becomes possible to obtain a channel region249 with a small electron trap density at the grain boundaries and inthe grains. As a result, a TFT type MOS transistor with superiorelectrical characteristics is obtained.

When the top gate construction TFT type MOS transistor 260 according tothis embodiment is used for an SRAM load device, for example, the powerconsumption of the SRAM is reduced. Further, the resistance of the SRAMto software errors is improved, so the reliability is improved. Further,the TFT type MOS transistor according to the present embodiment may besuitably used for a drive transistor of a liquid crystal display aswell.

The present invention will be explained below with reference to moredetailed examples. Note that the present invention is not limited tothese examples.

Example 1

First, an amorphous silicon film of a thickness of 80 nm was formed on aquartz substrate by the low pressure (LP) CVD method using monosilane(SiH₄). The deposition temperature was 500° C. Next, the excimer laserlight was irradiated on the amorphous silicon film to crystallize theamorphous silicon and obtain a polycrystalline silicon film. At thattime, the substrate was heated to 400° C. The surface treatmentapparatus used for the laser irradiation was a VEL of Sopra Co. with atotal energy of 10 J. The energy density of the laser was 280 mJ/cm².The number of shots was one and the range covered was 6 cm×6 cm.

Next, for observation by a transmission type electron microscope (TEM),the quartz substrate (SiO₂) was etched using a liquid mixture of HF:H₂O=1:1 to obtain just the polycrystalline silicon thin film (sample). Theresults of the TEM observation (bright-field image) at the substantialcenter portion of the sample are shown in FIG. 24. As the TEM, use wasmade of a JEOL 2000FX-II of an acceleration voltage of 200 kV.

Table 1 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 24.

                  TABLE 1                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Excimer Laser Energy Density in Case of Thickness of 80                       nm, Substrate Heating of 400° C., and Single Shot                                  Comp. Ex.                                                                     1         Ex. 1   Ex. 2                                           ______________________________________                                        Excimer laser 220         280     350                                         energy density                                                                (mJ/cm.sup.2)                                                                 Grain size range                                                                            (Amo.)      20-60   20-100                                      (nm)                                                                          Average grain size                                                                          (Amo.)       25      60                                         (nm)                                                                          ______________________________________                                    

Example 2

The same procedure was followed as in Example 1 to prepare a sampleexcept that the laser energy density was made 350 mJ/cm². TEMobservation was performed at the substantial center portion of thesample. The results of the TEM observation (bright-field image) areshown in FIG. 8.

Table 1 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 25.

Comparative Example 1

The same procedure was followed as in Example 1 to prepare a sampleexcept that the laser energy density was made 220 mJ/cm². TEMobservation was performed at the substantial center portion of thesample. The results of the TEM observation (electron diffractograph) areshown in FIG. 26.

The diffractograph of the photograph shown in FIG. 26 shows that thesample remains amorphous.

Evaluation

Comparing Examples 1 and 2 and Comparative Example 1, it was found that,as shown in the above-mentioned Table 1, at a thickness of 80 nm,Example 2, where the energy density was 350 mJ/cm², is preferable forobtaining a polycrystalline silicon thin film with a large grain size.

Example 3

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the timedeposition was made 40 nm and the laser energy density was made 300mJ/cm². TEM observation was performed at the substantial center portionof the sample. The results of the TEM observation (bright-field image)are shown in FIG. 25.

Table 2 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 27.

                  TABLE 2                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Excimer Laser Energy Density in Case of Thickness of 40                       nm, Substrate Heating of 400° C., and Single Shot                                  Comp. Ex.                                                                     2         Ex. 3   Ex. 4                                           ______________________________________                                        Excimer laser 150         300     350                                         energy density                                                                (mJ/cm.sup.2)                                                                 Grain size range                                                                            (Amo.)      50-200  50-200                                      (nm)                                                                          Average grain size                                                                          (Amo.)      150     150                                         (nm)                                                                          ______________________________________                                    

Example 4

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the timedeposition was made 40 nm and the laser energy density was made 350mJ/cm². TEM observation was performed at the substantial center portionof the sample. The results of the TEM observation (bright-field image)are shown in FIG. 25.

Table 2 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 28.

Comparative Example 2

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the timedeposition was made 40 nm and the laser energy density was made 150mJ/cm². TEM observation was performed at the substantial center portionof the sample. The results of the TEM observation (electrondiffractograph) are shown in FIG. 29.

The diffractograph of the photograph shown in FIG. 29 shows that thesample remains amorphous.

Evaluation

Comparing Examples 3 and 4 and Comparative Example 2, it was found that,as shown in the above-mentioned Table 2, at a thickness of 40 nm, anenergy density of 300 mJ/cm² is sufficient for obtaining apolycrystalline silicon thin film with a large grain size and that thereis not that great a difference even if the energy density is made higherthan that.

Example 5

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the timedeposition was made 80 nm, the laser energy density was made 350 mJ/cm²,and laser annealing treatment was performed without performing substrateheating (that is, at room temperature). TEM observation was performed atthe substantial center portion of the sample. The results of the TEMobservation (bright-field image) are shown in FIG. 30.

Table 3 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 30.

                  TABLE 3                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Number of Shots in Case of Thickness of 80 nm, No                             Substrate Heating (RT), and Excimer Laser Energy Density                      of 350 mJ/cm.sup.2                                                                        Ex. 5     Ex. 6   Ex. 7                                           ______________________________________                                        No. of shots   1          10      100                                         Grain size range                                                                            20-70       20-70   20-70                                       (nm)                                                                          Average grain size                                                                          40          40       40                                         (nm)                                                                          ______________________________________                                    

Example 6

The same procedure was followed as in Example 5 to prepare a sampleexcept that the number of shots of the laser irradiated on the samesample was made 10. TEM observation was performed at the substantialcenter portion of the sample. The results of the TEM observation(bright-field image) are shown in FIG. 31.

Table 3 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 31.

Example 7

The same procedure was followed as in Example 5 to prepare a sampleexcept that the number of shots of the laser irradiated on the samesample was made 100. TEM observation was performed at the substantialcenter portion of the sample. The results of the TEM observation(bright-field image) are shown in FIG. 32.

Table 3 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 32.

Evaluation

Comparing Examples 5 to 7, it was found that, as shown in theabove-mentioned FIGS. 30 to 32 and Table 3, the crystallinity and thegrain size of the polycrystalline silicon thin film are not dependent onthe number of shots. Accordingly, from the viewpoint of shortening ofthe production steps, a single shot of laser light is sufficient.

Example 8

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the time ofdeposition was made 40 nm. TEM observation was performed at thesubstantial center portion of the sample. The results of the TEMobservation (bright-field image) are shown in FIG. 33.

Table 4 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 33.

                  TABLE 4                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Thickness in Case of Substrate Heating of 400° C., Excimer             Laser Energy Density of 350 mJ/cm.sup.2, and Single Shot                                        Ex. 8 Ex. 9                                                 ______________________________________                                        Thickness (nm)       40     80                                                Grain size range (nm)                                                                             50-200  20-100                                            Average grain size (nm)                                                                           150     60                                                ______________________________________                                    

Example 9

The same procedure was followed as in Example 8 to prepare a sampleexcept that the thickness of the amorphous silicon film at the time ofdeposition was made 80 nm. TEM observation was performed at thesubstantial center portion of the sample. The results of the TEMobservation (bright-field image) are shown in FIG. 34.

Table 4 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 34.

Evaluation

Comparing Examples 8 and 9, it was found that, as shown in theabove-mentioned FIGS. 33 and 34 and Table 4, at conditions the sameexcept for the thickness, a small thickness of 40 nm is advantageous forobtaining a polycrystalline silicon thin film with a large grain size.

Example 10

The same procedure was followed as in Example 1 to prepare a sampleexcept that the thickness of the amorphous silicon film at the timedeposition was made 40 nm, the laser energy density was made 300 mJ/cm²,and laser annealing treatment was performed without performing substrateheating (that is, at room temperature). TEM observation was performed atthe substantial center portion of the sample. The results of the TEMobservation (bright-field image) are shown in FIG. 35.

Table 5 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 35.

                  TABLE 5                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Substrate Heating in Case of Thickness of 40 nm, Excimer                      Laser Energy Density of 350 mJ/cm.sup.2, and Single Shot                                        Ex. 10                                                                              Ex. 11                                                ______________________________________                                        Substrate heating   RT      400° C.                                    Grain size range (nm)                                                                             20-50   50-200                                            Average grain size (nm)                                                                           20      150                                               ______________________________________                                    

Example 11

The same procedure was followed as in Example 10 to prepare a sampleexcept that the substrate heating temperature was made 400° C. TEMobservation was performed at the substantial center portion of thesample. The results of the TEM observation (bright-field image) areshown in FIG. 36.

Table 5 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 36.

Example 12

The same procedure was followed as in Example 1 to prepare a sampleexcept that the laser energy density was made 350 mJ/cm² and laserannealing treatment was performed without performing substrate heating(that is, at room temperature). TEM observation was performed at thesubstantial center portion of the sample. The results of the TEMobservation (bright-field image) are shown in FIG. 37.

Table 6 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 37.

                  TABLE 6                                                         ______________________________________                                        Dependency of Polycrystalline Silicon Grain Size on                           Substrate Heating in Case of Thickness of 80 nm, Excimer                      Laser Energy Density of 350 mJ/cm.sup.2, and Single Shot                                        Ex. 12                                                                              Ex. 13                                                ______________________________________                                        Substrate heating   RT      400° C.                                    Grain size range (nm)                                                                             20-70   20-100                                            Average grain size (nm)                                                                           40      60                                                ______________________________________                                    

Example 13

The same procedure was followed as in Example 12 to prepare a sampleexcept that the substrate heating temperature was made 400° C. TEMobservation was performed at the substantial center portion of thesample. The results of the TEM observation (bright-field image) areshown in FIG. 38.

Table 6 shows the results when finding the range of the grain size andaverage grain size in the polycrystalline silicon film (sample) from thephotograph shown in FIG. 38.

Evaluation

As shown in the above-mentioned FIGS. 35 to 38 and Tables 5 and 6, whenthe only different condition was whether or not substrate heating wasperformed, it was found that a polycrystalline silicon film with alarger grain size can be obtained by performing substrate heating.

Further, the sample of Example 11 was examined as to the uniformity inthe shot plane of the range of grain size and the average grain size. Asa result, it was found that there was a tendency for the grains to belarge at the center and for the grain size to become somewhat smallerthan the center portion at the peripheral portions, but it was alsofound that this was of a range not posing a problem in the manufactureof a device.

As explained above, according to the method of formation of apolycrystalline silicon thin film of the present invention, it ispossible to obtain a polycrystalline silicon thin film with aconsiderably large average grain size and small electron trap density atthe grain boundaries and in the grains over a wide region of at least 3cm×3 cm (about 10 cm²) by a single annealing treatment. Accordingly, ifthe obtained polycrystalline silicon thin film is used for a medium orsmall sized direct-view type liquid crystal display etc., massproduction of high performance liquid crystal displays etc. becomespossible.

Further, according to the method of formation of a channel of atransistor according to the present invention, a transistor channel isformed in the polycrystalline silicon thin film formed by the method offormation of a polycrystalline silicon thin film, so the effect of thegrain boundaries in the channel and the electron traps becomes smaller.Accordingly, the leakage current can become smaller, the variation inthe threshold voltage greatly reduced, and the reliability of thetransistor greatly improved.

Further, there is the effect that it is possible to reduce the variationin characteristics of the transistors.

What is claimed is:
 1. A method of forming a thin layer of polycrystalline silicon having an average grain size of about 150 nm on a substrate comprising:forming an amorphous silicon layer having a thickness of from about 30 nm to about 50 nm on a substrate using monosilane (SiH₄) by a low pressure CVD method at a deposition temperature of less than about 500° C.; heating the amorphous silicon layer and substrate to a temperature of from about 350° C. to about 450° C.; irradiating the heated amorphous silicon layer in a single shot with excimer laser light having substantially uniform intensity in a diametrical direction of flux and having a total energy of at least 10 J, an energy density of from about 280 mJ/cm² to 330 mJ/cm² at a pulse width of from about 140 ns to about 200 ns, whereby a polycrystalline silicon thin film having an average grain size of about 150 nm and a low electron trap density at grain boundaries and in grains is provided over a region of at least about 6 cm×6 cm in a single annealing treatment.
 2. A method of forming a thin layer of polycrystalline silicon on a substrate, according to claim 1, further including a step of forming a light reflection prevention film on a surface of said amorphous silicon layer, before said heating and irradiating steps. 